1. Field of the Invention
The subject of the present invention is a process for monitoring traffic for automatic vehicle incident detection.
The application at which the invention is more particularly aimed relates to the monitoring of road or motorway traffic, conventionally referred to generically as Automatic Incident Detection (AID).
In this application it is sought especially to be able to detect a vehicle coming to a stop on traffic lanes or on hard shoulders. Other parameters may beneficially be supplied, such as the detection of holdups or the state of the traffic flow.
Monitoring the traffic on a road or motorway is very important since its aim is to improve the fluidity of the traffic and the safety of users. It is therefore paramount to know how to detect any incident or slowdown as quickly as possible so as to forewarn the users via variable-message road signs, thereby limiting the risks of pileups, and to involve the emergency services rapidly if necessary.
2. Discussion of the Background
The monitoring of road traffic is presently undertaken using various techniques which may be classed into two categories, on the one hand techniques based on pointwise analysis of a section of road or of motorway and, on the other hand, techniques based on overall analysis of this same section.
In the first case, only certain points of the road, located at predetermined distances from one another, are observed. Analysis of traffic parameters at these various points, such as the mean speed of the vehicles or the flow rate, makes it possible to detect, by applying special computational algorithms, the consequences of a possible incident between these points.
A first very widely used technology consists in placing induction loops under the road. The variation in the field induced in such loops makes it possible to ascertain whether a vehicle has or has not passed. The main advantage of this technology lies in the fact that the induction loops operate irrespective of climatic conditions, by day and by night. However, it is unwieldy and expensive to install these loops, and is difficult, or even impossible, to carry out maintenance or to replace loops in the event of a breakdown.
A second technology consists in video cameras located at the various points which one wishes to analyse over a given section, each camera being associated with an automatic processing of images. It is very simple to install the video cameras, but their performance is inconclusive since it depends strongly on the climatic conditions and on the lighting conditions. Furthermore, the algorithms used in image processing are complex and require considerable computational power.
To alleviate the problem of the climatic conditions, a third known technology, again implementing a technique of pointwise analysis of a section of road or of motorway, employs a radar, either a continuous-wave stationary or pulsed Doppler radar. A technique which uses a continuous-wave stationary radar to extract various parameters, such as speed or length, is for example described in the document U.S. Pat. No. 4,985,705. Moreover, refer to the document FR 2,695,742 filed by the Applicant for the description of a pulsed Doppler radar, whose particular positioning and associated algorithm make it possible to extract various parameters (especially the number of vehicles per traffic lane, the speed of the vehicles, the length of the vehicles).
The major drawback of the three technologies above, based on pointwise analysis of a section of road, is that detection of an incident is not immediate. Indeed, an incident occurring near an analysis point is not detected; rather, only the later consequences of this incident at the measurement point are detected. The detection timescale may be very long, of the order of several minutes.
As we stated earlier, a second presently known analysis technique consists in undertaking an overall analysis of a section of road or motorway, by monitoring this section over a zone of several hundred meters, and to do so in such a way as to detect the incidents almost instantaneously. A single technology, still at the development stage, implements this technique by using a video camera associated with image processing specific to AID. The drawbacks are a detection range, hence a monitoring zone, limited to a few hundred meters, and which may be greatly reduced in the event of poor weather (rain, snow, fog) or lighting conditions, that is to say when the risks of an incident are greatest.